System and method for compensating for power loss due to a radio frequency (RF) signal probe mismatch in conductive signal testing

ABSTRACT

System and method for compensating for power loss due to a radio frequency (RF) signal probe mismatch in conductive RF signal testing of a RF data signal transceiver device under test (DUT). Sourcing the RF test signal with the RF vector signal transceiver at multiple test frequencies enables isolation of and compensation for power loss due to a mismatch between the RF signal probe and RF DUT connection based on predetermined losses of the RF signal path.

BACKGROUND

The present invention relates to compensating for power loss of a radiofrequency (RF) signal probe mismatch in conductive signal testing of aRF data signal transceiver, and in particular, to compensating for suchpower loss during conductive signal testing.

Many of today's electronic devices use wireless signal technologies forboth connectivity and communications purposes. Because wireless devicestransmit and receive electromagnetic energy, and because two or morewireless devices have the potential of interfering with the operationsof one another by virtue of their signal frequencies and power spectraldensities, these devices and their wireless signal technologies mustadhere to various wireless signal technology standard specifications.

When designing such wireless devices, engineers take extra care toensure that such devices will meet or exceed each of their includedwireless signal technology prescribed standard-based specifications.Furthermore, when these devices are later being manufactured inquantity, they are tested to ensure that manufacturing defects will notcause improper operation, including their adherence to the includedwireless signal technology standard-based specifications.

Testing of such wireless devices typically involves testing of thereceiving and transmitting subsystems of the device under test (DUT).The testing system will send a prescribed sequence of test data packetsignals to a DUT, e.g., using different frequencies, power levels,and/or signal modulation techniques to determine if the DUT receivingsubsystem is operating properly. Similarly, the DUT will send test datapacket signals at a variety of frequencies, power levels, and/ormodulation techniques for reception and processing by the testing systemto determine if the DUT transmitting subsystem is operating properly.

For testing these devices following their manufacture and assembly,current wireless device test systems typically employ testing systemshaving various subsystems for providing test signals to each deviceunder test (DUT) and analyzing signals received from each DUT. Somesystems (often referred to as “testers”) include, at least, one or moresources of test signals (e.g., in the form of a vector signal generator,or “VSG”) for providing the source signals to be transmitted to the DUT,and one or more receivers (e.g., in the form of a vector signalanalyzer, or “VSA”) for analyzing signals produced by the DUT. Theproduction of test signals by the VSG and signal analysis performed bythe VSA are generally programmable (e.g., through use of an internalprogrammable controller or an external programmable controller such as apersonal computer) so as to allow each to be used for testing a varietyof devices for adherence to a variety of wireless signal technologystandards with differing frequency ranges, bandwidths and signalmodulation characteristics.

The testing environment may include one or both of two general forms ofRF signal conveyance: (1) conductive, or wired, and/or (2) radiative, orwireless. In the case of the former (typically implemented as a co-axialcable with a signal conductor surrounded by a grounded conductor actingas a shield against external electromagnetic interference), oneimportant characteristic is that of signal path loss through theconductive signal path. Another is that of signal reflections and powerloss due to mismatches caused by the RF signal probe that connects tothe DUT between the impedances of the conductive signal path andconductive signal connector of the DUT. While the actual techniques usedto determine signal path loss and/or probe mismatches are simple, theyhave required interruption and re-configuration of the RF signalconnections as part of the test operations, e.g., prior to and/or duringeach test sequence. This results in longer test times and increasedtesting costs due to such time delays as well as potential repairs orrework of signal connections.

SUMMARY

System and method for compensating for power loss due to a radiofrequency (RF) signal probe mismatch in conductive RF signal testing ofa RF data signal transceiver device under test (DUT). Sourcing the RFtest signal with the RF vector signal transceiver at multiple testfrequencies enables isolation of and compensation for power loss due toa mismatch between the RF signal probe and RF DUT connection based onpredetermined losses of the RF signal path.

In accordance with example embodiments, a system for compensating powerloss of a radio frequency (RF) signal probe used in conductive RF signaltesting of a device under test (DUT) includes: a RF vector signaltransceiver responsive to one or more transceiver control signals bygenerating one or more outgoing RF signals and time domain processingone or more incoming RF signals; a RF signal probe to convey the one ormore outgoing RF signals and the one or more incoming RF signals to andfrom, respectively, a DUT; a conductive RF signal path connected to andbetween the RF vector signal transceiver and the RF signal probe viafirst and second signal path ends, respectively, to convey the one ormore outgoing RF signals and the one or more incoming RF signals; one ormore processors coupled to communicate with the RF vector signaltransceiver; and one or memory devices coupled to the one or moreprocessors and comprising a non-transitory computer readable mediumcontaining a plurality of computer readable instructions. When executedby the one or more processors, the computer readable instructions causethe one or more processors to provide the one or more transceivercontrol signals such that: the one or more outgoing RF signals comprisean iterative plurality of mutually distinct RF signal frequencies with asingle frequency tone; the one or more incoming RF signals comprise aplurality of reflected RF signals from the RF signal probe and relatedto at least a portion of the one or more outgoing RF signals; and thetime domain processing one or more incoming RF signals includescomputing a plurality of measured signal magnitudes of the plurality ofreflected RF signals, and computing a plurality of net signal magnitudesof the plurality of reflected RF signals reduced by corresponding onesof a plurality of predetermined path losses of the conductive RF signalpath corresponding to the plurality of mutually distinct RF signalfrequencies.

In accordance with further example embodiments, a method forcompensating power loss of a radio frequency (RF) signal probe used inconductive RF signal testing of a device under test (DUT) includes:responding, with a RF vector signal transceiver, to one or moretransceiver control signals by generating one or more outgoing RFsignals and time domain processing one or more incoming RF signals;conveying the one or more outgoing RF signals and the one or moreincoming RF signals via a RF signal probe to and from, respectively, aDUT; conveying the one or more outgoing RF signals and the one or moreincoming RF signals via a conductive RF signal path that is connected toand between the RF vector signal transceiver and the RF signal probe viafirst and second signal path ends, respectively; and communicating withthe RF vector signal transceiver by accessing and executing a pluralityof computer readable instructions. Execution of the computer readableinstructions cause the one or more transceiver control signals to beprovided such that: the one or more outgoing RF signals comprise aniterative plurality of mutually distinct RF signal frequencies with asingle frequency tone; the one or more incoming RF signals comprise aplurality of reflected RF signals from the RF signal probe and relatedto at least a portion of the one or more outgoing RF signals; and thetime domain processing one or more incoming RF signals includescomputing a plurality of measured signal magnitudes of the plurality ofreflected RF signals, and computing a plurality of net signal magnitudesof the plurality of reflected RF signals reduced by corresponding onesof a plurality of predetermined path losses of the conductive RF signalpath corresponding to the plurality of mutually distinct RF signalfrequencies.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a common test environment for conductive RF signaltesting.

FIG. 2 depicts a test environment for conductive RF signal testing inaccordance with example embodiments.

FIG. 3 depicts design and use of signal data filters in accordance withexample embodiments.

FIG. 4 depicts a comparison of empirical test data using a conventionalOSL technique and a technique in accordance with example embodiments.

FIG. 5 depicts a test environment for conductive RF signal testing inaccordance with example embodiments.

FIG. 6 depicts a comparison of empirical test data using a conventionalRF power meter and an SMA co-axial connector as the RF probe inaccordance with example embodiments.

FIG. 7 depicts a time relationship between corresponding incident andreflected RF signals.

DETAILED DESCRIPTION

The following detailed description is of example embodiments of thepresently claimed invention with references to the accompanyingdrawings. Such description is intended to be illustrative and notlimiting with respect to the scope of the present invention. Suchembodiments are described in sufficient detail to enable one of ordinaryskill in the art to practice the subject invention, and it will beunderstood that other embodiments may be practiced with some variationswithout departing from the spirit or scope of the subject invention.

Throughout the present disclosure, absent a clear indication to thecontrary from the context, it will be understood that individual circuitelements as described may be singular or plural in number. For example,the terms “circuit” and “circuitry” may include either a singlecomponent or a plurality of components, which are either active and/orpassive and are connected or otherwise coupled together (e.g., as one ormore integrated circuit chips) to provide the described function.Additionally, the term “signal” may refer to one or more currents, oneor more voltages, or a data signal. Within the drawings, like or relatedelements will have like or related alpha, numeric or alphanumericdesignators. Further, while the present invention has been discussed inthe context of implementations using discrete electronic circuitry(preferably in the form of one or more integrated circuit chips), thefunctions of any part of such circuitry may alternatively be implementedusing one or more appropriately programmed processors, depending uponthe signal frequencies or data rates to be processed. Moreover, to theextent that the figures illustrate diagrams of the functional blocks ofvarious embodiments, the functional blocks are not necessarilyindicative of the division between hardware circuitry.

Referring to FIG. 1 , a common test environment 10 a for conductive RFsignal testing includes a tester 12 (e.g., a VSG and VSA combination, ora vector transceiver), and a conductive RF test signal path 14 toconnect to the DUT 16. The signal path 14 may include one or more RFcables and fixture(s) 15 a connected to the tester 12 via a RF connector15 b and to the DUT 16 via another RF connector 15 c. In order to testthe DUT 16 accurately RF signal loss of the signal path 14 must bedetermined to enable accurate measurements of signals received by andfrom the DUT 16. Three techniques for doing this currently predominate.

One method includes use of a RF signal source (e.g., the tester 12)connected via the RF signal path 14 to a power meter (not shown), inplace of the DUT 16, to measure an absolute power difference betweenwhat the power meter receives and the known signal power from thesource. However, this requires a high accuracy of the measureddifference between the source and power meter, as well as reconfiguringthe DUT testing arrangement to connect the signal source and power metervia the signal path 14.

A second method includes use of a two-port vector network analyzer (VNA,not shown) in place of the tester 12 with two ports at each connection15 b, 15 c to the RF signal path 14 to measure insertion loss (oftenreferred to as S21 in S-parameters terms) more directly. So, thisrequires more expensive test equipment, e.g., a VNA, as well as alsoreconfiguring the DUT testing arrangement to connect to the VNA.

A third method includes use of the tester 12 at one connection 15 b tothe RF signal path 14 and uses of an open circuit connection (OPEN), ashorted circuit connection (SHORT), and a load connection (LOAD) havingthe appropriate characteristic impedance of the RF system being tested(e.g., 50 ohms resistive) each time at the other connection 15 c toenable measurements of return loss for each terminal connection (OPEN,SHORT and LOAD). All three measured results may then be used tocalculate the path loss. This has the effect of effectively using thenormal DUT testing arrangement_as an emulated vector network analyzer(VNA) to measure return loss (S-parameter S11). Modern VSA/VSG systemsmay also perform such a measurement if they support simultaneous VSG/VSAoperation and perform appropriate processing of the transmitted andreceived signals. While this method may enable maintaining the DUTtesting arrangement, it still requires designing special connectors forthe OPEN, SHORT and LOAD measurements as well as three operations toswitch among these three special connectors. (This is often referred toas the OSL method.)

The disadvantages of these methods may be avoided using systems andmethods of currently disclosed example embodiments. As discussed in moredetail below, a vector transceiver (e.g., a tester 12) connects to theinput 15 b of the RF signal path 14 and an OPEN connects at the output15 c. Advantages include maintaining the DUT testing arrangement andavoiding need for additional or different test equipment, thereby savingoperation time and cost. Further, while a special OPEN connector may behelpful, it should not be necessary since one may instead simply theoutput connection 15 c of the RF signal path 14 unterminated and therebyserving as an OPEN. In most automated testing arrangements a RF signalprobe may be used at the end of the cable which may serve as an OPENconnection when unterminated e.g., not connected to a load such as aDUT.

Referring to FIG. 2 , a test environment 10 b for conductive RF signaltesting in accordance with example embodiments includes the tester 12(e.g., vector signal transceiver), and the conductive RF test signalpath 14 that includes one or more RF cables and fixture(s) 15 aconnected to the tester 12 via an input RF connector 15 b and an outputRF connector 15 c. However, when testing for path losses, the output RFconnector 15 c may remain unterminated to provide an OPEN connection 15cc.

As an optional initial procedure one may establish or otherwisedetermine information about the testing hardware configuration(s) beingused. For example, such information may include details about the RFsignal path 14, such as the number of interconnected cables, length ofeach cable, how many connectors are in place, etc. As noted, instead ofconnecting the output connector 15 c to the DUT 16, either a RF OPENconnector is connected or the output connector 15 c is left unconnected(i.e., unterminated)

A range of RF test signal frequencies to be measured (e.g., withcorresponding frequency margins) may be selected or defined based onintended or anticipated DUT operations. The vector signal transceivertester may be programmed or otherwise controlled to provide (e.g.,generate and emit), with its transmitter, a single DC tone at thebaseband frequency for each of the RF test signal frequencies, andenable its receiver to capture a corresponding return signal for each ofthe RF test signal frequencies. Captured I/Q signal samples may beaveraged over time capture to compute a single complex number. Iteratingthese steps of transmitting incident signals and capturing reflectedsignals over portions or all of the defined range of frequencies mayenable computation of an array of complex numbers, each of whichcorresponds to a respective one of the defined frequencies. Such complexnumerical array may be processed in accordance with known principles tocalculate a path loss for each frequency to be measured.

Referring to FIG. 3 , this processing 20 may include steps by which thereturn signal data 21 may be processed 22 to extract time or distanceinformation 23 (discussed in more detail below) for use in designing afilter 24, the characteristics 25 of which may be used to filter 26 thereturn signal data 21. The filtered return signal data 27 may beaveraged to compute 28 absolute path loss 29 for the frequency beingtested. Such processing 20 may be structured or applied from theperspective of either a distance domain or frequency domain toeffectively serve the same purpose, e.g., by processing, filtering andaveraging measured signal data that is processed along the way ascorresponding to distances (e.g., traversed by the incident and/orreflected signal pulses) or frequencies (e.g., of the incident and/orreflected signals).

Referring to FIG. 4 , a linear graph of empirical test results ofmeasured path losses over a frequency range from below 1 GHz to morethan 5 GHz using a conventional OSL method and a method in accordancewith example embodiments as discussed above demonstrates how closely themore advantageous techniques discussed herein produce test resultsclosely tracking those of conventional OSL techniques.

As noted above, conventional path loss measurement and compensationtechniques fail to account much less compensate for additional signalloss(s) at the RF probe that connects to the DUT, thereby effectivelyassuming that perfect matching exists between the RF probe and the RFconnector on the DUT. However, since successfully connecting the RFprobe to the DUT primarily relies upon a mechanical operation and iscontrolled by application of appropriate physical forces. Hence, soonafter multiple connections have been made and removed, associatedchanges in surface abrasions and application forces, cause degradationsin the matching between the RF probe to the DUT connector. This resultsin further power losses in the signal path that will not be detected orcompensated by path loss measurements alone as discussed above. Suchadditional power losses caused by such RF probe connector mismatches mayresult in a higher rate of re-testing DUTs, which, in turn, requiresadditional instances of DUT connections and may lead to reducedmanufacturing yield rates.

Referring to FIG. 5 , a test environment 40 for detecting and enablingcompensation for RF probe mismatched when performing conductive RFsignal testing in accordance with example embodiments includes a tester42 (e.g., VSG/VSA combination or vector signal transceiver), and aconductive RF test signal path 44 to enable connection to the DUT 16.The signal path 44 may include one or more RF cables and fixture(s) 45 aconnected to the tester 42 via a RF connector 45 b and to the DUT 16 viaa RF probe assembly 45 c. Connection to the DUT 16 is completed via aninput RF probe connector 45 cb, the RF probe 45 ca and an output RFprobe connector 45 cc that, in turn, connects to a RF connector 17 ofthe DUT 16.

As discussed in more detail below, in accordance with exampleembodiments, compensation may be provided for power loss of RF probemismatches in conductive RF signal testing by measuring the returnsignal to estimate the reflection signal caused by the RF probemismatches and, in turn, account for such reflection as an additionalsignal path power loss. Advantages include maintaining the DUT testingconfiguration since any additional power loss may be measured with theDUT remaining in its desired testing configuration. Full control may beretained by the tester since DUT control action is unnecessary.Compensation for such additional power loss may be provided followingeach DUT insertion into the testing configuration, thereby increasingaccuracy of the DUT RF test.

This process may be performed by first connecting the DUT to the RFprobe. This may be preceded by, followed by or performed concurrentlywith defining specific frequencies at which measurements are to beperformed. The vector transceiver tester may transmits a single DC toneat the baseband signal frequency while any resulting reflections of suchincident signal transmissions may be captured by the receiver of thetester. An average over time of the captured I/Q samples may be computedto provide a single complex number. Such incident signal transmissions,reflected signal captures and average computations may be iterated overthe defined range of frequencies. Finally, the computed complex numbersmay be processed to determine the reflection signal caused by RF probemismatches.

This processing of the computed complex numbers to determine thereflection signal caused by RF probe mismatches may be performed inconjunction with RF signal path loss data determined previously with theconventional OSL method discussed above. This will allow removal of RFsignal path effects of the original test configuration, with anyremaining loss(s) to be attributed to reflection signals caused by RFprobe mismatches and compensated. Alternatively, such processing may beperformed in conjunction with RF signal path loss data determined byusing the technique discussed above in which an OPEN (e.g.,unterminated) RF signal path end connection is used with a vectortransceiver tester to extract the reflection signals from the RF probecaused by matching issues. If the reflection signal exceeds or otherwisetransverses a predetermined threshold, testing may be aborted to enablesuch issues to rectified or otherwise resolved. Otherwise, compensationfor the added power loss may be applied by the tester while DUT RFtesting continues.

Referring to FIG. 6 , a linear graph of empirical test results ofmeasured path losses due to RF probe reflections over a frequency rangefrom below 1 GHz to nearly 6 GHz using a conventional power meter methodand a method in accordance with example embodiments as discussed abovedemonstrates how closely the more advantageous techniques discussedherein produce test results closely tracking those of conventional powermeter techniques.

Referring to FIG. 7 , as noted above, these operations may be performedfrom the perspective of time or distance domains. As depicted here, aswill be readily appreciated by one of ordinary skill in the art,interrelatedness of processing in the time and distance domains may bemore readily understood in view of the fact that the reflected signalpulse will be captured by the receiver of the tester after a time delayΔT that is known to be related to the distance over which the reflectedsignal pulse must travel following transmission of the incident signalpulse.

Various other modifications and alternatives in the structure and methodof operation of this invention will be apparent to those skilled in theart without departing from the scope and the spirit of the invention.Although the invention has been described in connection with specificpreferred embodiments, it should be understood that the invention asclaimed should not be unduly limited to such specific embodiments. It isintended that the following claims define the scope of the presentinvention and that structures and methods within the scope of theseclaims and their equivalents be covered thereby.

What is claimed is:
 1. An apparatus including a system for compensatingpower loss of a radio frequency (RF) signal probe used in conductive RFsignal testing of a device under test (DUT), comprising: a RF vectorsignal transceiver responsive to one or more transceiver control signalsby generating one or more outgoing RF signals and time domain processingone or more incoming RF signals; a RF signal probe to convey said one ormore outgoing RF signals and said one or more incoming RF signals to andfrom, respectively, a DUT; a conductive RF signal path connected to andbetween said RF vector signal transceiver and said RF signal probe viafirst and second signal path ends, respectively, to convey said one ormore outgoing RF signals and said one or more incoming RF signals; oneor more processors coupled to communicate with said RF vector signaltransceiver; and one or memory devices coupled to said one or moreprocessors and comprising a non-transitory computer readable mediumcontaining a plurality of computer readable instructions that, whenexecuted by said one or more processors, cause said one or moreprocessors to provide said one or more transceiver control signals suchthat said one or more outgoing RF signals comprise an iterativeplurality of mutually distinct RF signal frequencies with a singlefrequency tone, said one or more incoming RF signals comprise aplurality of reflected RF signals from said RF signal probe and relatedto at least a portion of said one or more outgoing RF signals, and saidtime domain processing one or more incoming RF signals comprisescomputing a plurality of measured signal magnitudes of said plurality ofreflected RF signals, and computing a plurality of net signal magnitudesof said plurality of reflected RF signals reduced by corresponding onesof a plurality of predetermined path losses of said conductive RF signalpath corresponding to said plurality of mutually distinct RF signalfrequencies.
 2. A method for compensating power loss of a radiofrequency (RF) signal probe used in conductive RF signal testing of adevice under test (DUT), comprising: responding, with a RF vector signaltransceiver, to one or more transceiver control signals by generatingone or more outgoing RF signals and time domain processing one or moreincoming RF signals; conveying said one or more outgoing RF signals andsaid one or more incoming RF signals via a RF signal probe to and from,respectively, a DUT; conveying said one or more outgoing RF signals andsaid one or more incoming RF signals via a conductive RF signal paththat is connected to and between said RF vector signal transceiver andsaid RF signal probe via first and second signal path ends,respectively; and communicating with said RF vector signal transceiverby accessing and executing a plurality of computer readable instructionsto provide said one or more transceiver control signals such that saidone or more outgoing RF signals comprise an iterative plurality ofmutually distinct RF signal frequencies with a single frequency tone,said one or more incoming RF signals comprise a plurality of reflectedRF signals from said RF signal probe and related to at least a portionof said one or more outgoing RF signals, and said time domain processingone or more incoming RF signals comprises computing a plurality ofmeasured signal magnitudes of said plurality of reflected RF signals,and computing a plurality of net signal magnitudes of said plurality ofreflected RF signals reduced by corresponding ones of a plurality ofpredetermined path losses of said conductive RF signal pathcorresponding to said plurality of mutually distinct RF signalfrequencies.